Mechanical, centrifugal clutches are well known. They have found applications in a variety of mechanisms and devices where it is desired to transfer torque, or rotational force, from a driving member to a driven member only after the driving member has reached a desired rotational speed. At the desired rotational speed, centrifugal force applied to frictional elements associated with the driving member cause the frictional elements to move outwardly and engage a complementary surface of the driven member, thereby coupling the driving member to the driven member. As a result, the torque, or rotational force, of the driving member is transferred to the driven member. Clutches of this type are employed, for example, in brush cutters, hedge trimmers and other kinds of equipment for the maintenance of shrubs, trees and lawns.
A particular centrifugal clutch disclosed in the prior art is the subject of U.S. Pat. No. 2,027,970. The frictional elements, or clutch shoes, disclosed in that patent have frictional linings that engage an annular flange of a driven member when the rotational speed of the driving member reaches a desired level, thereby coupling a driving member to the driven member. The clutch of U.S. Pat. No. 2,027,970 includes a feature, typically, not incorporated in prior art clutches. Specifically, the furthest outward extent to which the clutch shoes can move is limited. This provides certain benefits. For example, the outward movement of the clutch shoes can be limited to prevent the frictional linings from wearing all the way through to the shoe surfaces on which the linings are mounted.
Whatever may be its advantages, the clutch disclosed in U.S. Pat. No. 2,027,970 tends to be cumbersome and complex. In particular, the clutch shoes cannot move independently of one another and the clutch requires a driving member somewhat elaborate in its construction. Thus, holes are formed in the sides of the clutch shoes in a: direction that extends, generally, circumferentially of the shoes. Pins are inserted in the adjacent sides of adjoining shoes. As the shoes are caused to move outwardly under the influence of centrifugal force, each shoe must follow the movements of the shoes adjoining it. Lugs, or stops, are incorporated in the driving member at locations such that, as the shoes continue to move outwardly, the pins will encounter respective lugs and further movement of the shoes is barred.
Despite the relatively highly-developed state of the art with respect to mechanical centrifugal clutches, there remains a need for a clutch construction that is simple, compact, of a lower cost to manufacture and of improved strength and wherein the outward extent to which the clutch shoes can move under the influence of centrifugal force is limited. The present invention satisfies that need. In addition, the present invention provides a more unified clutch construction through the conjoining of the various elements that make up the clutch.